This project deals with both the laboratory and clinical aspects of infection caused by the intestinal nematode, Strongyloides stercoralis. The laboratory research involves analysis and characterization of parasite antigens. The clinical studies focus upon the immune response of infected individuals, and factors that influence the immune response. For certain purposes experimental infections are carried out in the jird (Meriones unguiculaius). The diagnosis of chronic strongyloides infection is often difficult because excretion of larvae is scanty and intermittent. Therefore, an ELISA type of serologic test is useful in identifying individuals who harbor the parasite. But this serologic test is available only in specialized laboratories and availability of the antigen is limited. For these reasons, a cDNA library was prepared from infective (L3) larvae of the parasite, and several recombinant clones were identified by screening the library with immune serum of patients. Some of the clones, alone or in combination, can be used as diagnostic antigens in an ELISA test. Since some of the recombinant antigens are reactive with parasite-specific serum IgE, it may be possible to use them in an immediate hypersensitivity skin test. Several systems for expression of recombinant proteins, including yeast cells, are used. Brazilian patients with all combinations of infection with S. stercoralis and HTLV-1 retrovirus are studied to determine cytokine responses of peripheral blood mononuclear cells (PBMCs) to S.stercoralis antigen and mitogens. Blood samples are also obtained to check HTLV-1 and strongyloides serology, as well as serum IgE levels. PBMCs are also cultured and treated with special reagents so they can be fixed and frozen for analysis of intracellular cytokines.